Milliampere-seconds relay for radiographic control systems



March 13, 1951 .A. W. VINGERHOETS MILLIAMPERE-SECONDS RELAY FOR RADIOGRAPHIC CONTROL SYSTEMS Filed May 4, 1946 AGEN T Patented Mar. 13, i951 r'NHLLIAmERE-SECONIIS REDAY :FR .'-RADIQGRAPHIC CONTROL .SYSTEMS Antonius Wilhelmus Vingerhoets, Eindhoven,

llsetlnerlands,assigner, by -mcsne assignments,

to 'Hartford National Bank and Trust Company, iHartford, Conn., as trustee AppiicationMay y4, 1946,k Serial No.. 667,444 ."In'the NetherlandsfMarch '4, 1942 SectionL-Public Law 690, fAug-ust 8,1946 .Patent expires March ,4,519.62

( Cl. Z50-95 -,of current Vand time-.in a circuit supplying-.current to a load.

In certain elds'of'the electrical engineering, such as the X-rayindustry andthe Vwelding industry, use vis madeof devices for measuring a given integral value :of :the product of current and time. Periodically, :on reaching-this value expressed in amperefsecondsor-if this unit is too largen milliarnpereseconds, the current must be switched off. .-'I-hisswitching operation may be eiiected automatically. f

- Generally, a condenser is @used in .the-.measuringdevice. Thevoltage at-'thezcondenser is, proportional to its Y charge ande hence to ,the integral product to be measured. The value ofthisproduct can'be vread on Lafmeter which registers'this voltage and,` as an alternative, fthecondenserfmay be caused to-act `asa sourceof fvoltage on'a relay which responds' to afgi-ven voltage.andactszon a switch by means of which the currentiszcut off in the load circuit.

`It is obvious vthat the capacity ofthe-measuring condenser should be large enoughsforthe lvoltage which corresponds with the charge -to be measured at intervals lto Vbeonlylaiinegligiblepartici theoperating Voltage .because theoutput ofthe main source of .current wouldriotherwise.fall'considerably during .the .charging of .thecondensen In the case of an excessivelylow Acapacity the measuring condenser .would .readily develop an excessive counter-.electromotive force.

In certain cases Vitis only lpossible vtn satis'fy this requirement by a very"high capactyandfor this reason the method has been adopted-both with Xfray apparatus and with welding machines not`to connect the measuring .condenser directly .intoithe load circuit butto feed the charging -currrent to itacross a transformer whoseprimary is primary. vIt is thus ensured'that the jcounter voltage 'inthe 'load' circuit is lower 'than the .condenser'voltage Aand that as a resultthereof the Icapacity of the measure condenser -can'be kept vwithin-reasonable limits.

VA disadvantage of this method isthat it is inoperable for Vpure direct current. Even `for `pulsating direct current fit is not particularly :suitable on `account of'the'disadvantage attending 'the transfer oftliisfcurrent by means `of a transformer. The invention'relatestoa different lmeans :of #keeping ithe capacity of Y`the imeasure ance. hi-ghi.- comparedwith-theiballastresistance soithat 2 lcondenser Vsuiiiciently-lmv inthecase of .-a given admissible counter-voltage due-to -vwhich-the-.disadvantage of the -wellknown method ydoes not anse.

According to therinvention, a ballast resistance included in theloacl circuit-and of lowvaluencompared with the total resistance of ythe-load circuit hasconnected to it Atwo or more vpoints'of the charging circuitv of the measuringI condenser;y this connection being effected in such manner athat the charging current is substantially proportionalto the voltageidropfinthelballast resistance. VFrom the latter "condition:itiollowsthat it/is not suicientl simply to.` shunt theacondenser -by the: ballast resistance. YIn this ,cases the. counter voltage-would also be boundfto 2a suitable limit by'the resistance, but apart -from1thejfactzthat frequently in fthis case a ihigher r capacity-:than vis desirable would neverthelessl be rrequiredA for-f other reasons the Voltage at-the-condenser :wouldnot be proportionate'at all to-Ythelnumb'er loffmil'liampereseconds of the,` current 'in the.` load "'circuit.

In the simplest 'form of y"construction-of the device according to the inventionzthe Ameasure condenser has `aresistance .connected -withfit in series -and Vthe series+combination :of resistance and condenser is shunted by the ballastresist- This series-connectederesistance :must be the charging condition of the #measuring .e'ondenser has little iniiuenceonthefdistribution of the current over thetwobranches. Thisensures the advantage thatV a condenser off-low'capacity can be used land .nevertheless the voltage curve cutsthe line that designates the final valuezo'f-y the voltage under a favourable angle.

In order ,to ensure-:thatin spite of-.the-Y countervoltage which-thecondenser exerts; in theqchargingcircuit with a/ progressingV charge. the charging current yonly -varies proportionately .-to fthe c load Y current,-thevoltagefdrop in the ballastresistance quently'variable.

`In-`all cases lin which the v'condenser is charged by part of the load-*current'thezmeasuringvoltage is lower lthan Ythe 'voltage-fdrop in the :ballast resistance. It may be ydesirable :to Aoperate with a V`higher--measure'voltageinview"of the relay-used (Whose function ma'ycbe performedbyfadischarge "this tube on the cathode side. resistance is connected to the negative end of the ballast resistance and the grid of the electron grid voltage.

The idea is that the charging current rises and falls exactly in the same ratio as the main current and hence that in the presence of an electron discharge tube the anode current of this tube which is also the charging current of the measuring condenser is proportionate to the grid voltage which in turn is proportionate to the current in the ballast resistance. The accuracy may be assisted by using feedback coupling on the grid of the electron tube. This may be ensured by connecting a resistance in series with If the end of this valve to a further point of the ballast resistance the latter supplies a positive and the other resistance a negative component of the grid voltage. As is known per se a negative grid voltage Droportionate to the anode current permits of achieving proportionality of anode current and positive rents in the ballast resistance and the condenser branch is substantially determined by the ratio of the resistances and does not alter by reason of the characteristic curve of the electron valve or the charging condition of the measure condenser.

In order that the invention may be clearly understood and readily carried into effect three circuit diagrams will be described more fully as examples of devices according to the invention used in radiographic apparatus.

Figure 1 shows a device in which the load current is distributed over two resistances.

Figure 2 is the diagram of a device comprising a control tube, and

Figure 3 is the diagram of a device in which the charging current is supplied by a separate source of current.

' In all the figures, I designates an X-ray tube and 2 a triode which is connected in series there- Vwith and which may be used for controlling the current that passes through the X-ray tube.

In the diagram of Figure 2 a triode E serves as a series resistance for the condenser. The influence of the counter-voltage of the condenser on the charging current is thus decreased because the intensity of the charging current is not solely determined in the present case by the difference of the voltages at the ballast resistance and the condenser but in the rst place by the grid voltage of the triode 6. This voltage varies with the current in the resistance 3 due to the fact that the cathode of the triode is connected to the vnegative end of the resistance 3 and the In this case, the ratio of the curgrid to a tap 1 thereof. The measuring voltage establishing across condenser 4 may be indicated by a suitable Voltmeter circuit l5 or utilized to actuate a relay circuit I6 adapted to apply cutofl bias from battery Il on the grid of triode 2 when the measuring voltage has attained a predetermined magnitude. Meter !5 is preferably calibrated in milliampereseconds.

A higher condenser voltage may be obtained by connecting a separate source of current, as shown in Figure 3, which source of current may comprise a transformer and rectifier to be connected between the points 8 and for the supply of the measuring condenser 4. In this case the Voltage at the ballast resistance 3 only serves for the control of the charging current. A separate source of charging current also has the advantage that the voltage drop in the ballast resistance'can be rendered altogether independent of the condenser voltage, thus being purely proportional to the current in the load circuit. As in the embodiment of Fig. 2, the measuring voltage attained by condenser 4 may be indicated by voltmeter l5 or maybe utilized to actuate relay circuit l6 which serves to connect a cut-off bias to the grid of triode 2 when the voltage across condenser 4 has risen to a predetermined value.

The tapping in the resistance 3 may be made variable and this permits of choosing at will the number of milliampereseconds at which the relay to be connected to the condenser responds.

In order that the influence of the condenser voltage on the charging current may be eliminated even more satisfactorily the triode is replaced in Figure 3 by a screen-grid valve tube. The screen grid is given a constant positive voltage derived from the potentiometer H. Variations in this voltage due to the supply with alternating current are absorbed by a condenser l2.

A source of voltage I3 serves to cause the tube I0 to operate in the suitable point of its characteristic curve.

In the diagrams of Figures 2 and 3 care is taken that the shape of the characteristic curve of the tubes 6 and l0 does not detract from the proportionality of the charging current and the current in the resistance 3 by including a resistance I4 between the cathode of the control valve and the negative end of the resistance 3. Due to the voltage drop in this resistance feedback coupling is set up on the grid of the valve and the influence of the curvature of the characteristic curve of the tube is eliminated so that the charging current continues proportional to the main current within wide limits.

What I Vclaim is:

1. A system for developing a measuring voltage proportional to the integral value of the product of current and time in a load circuit, said system comprising a resistance serially connected to said load circuit, the'voltage developed across said resistance depending on the intensity of current ow in said load circuit, the value of said resistance being low relative to the resistance of said load circuit, an integrating network including a capacitance connected in series with an electron discharge tube having a cathode, a control electrode and an anode, means to apply a charging potential across said network, and means to apply a portion of the voltage developed across said resistance between said cathode and said control electrode to control the charging current of said network substantially in proportion to the voltage developed across said resistance, whereby a measuring voltage is developed Aacross said capacitance.

2. Apparatus for measuring thevinteg-ral value of the product of current and time-in a load circuit, said apparatus comprising a resistance serially connected to said load circuit, the volt- Vage developed across said resistance depending on the intensity of current flow in said load circuit, thevalue of said resistance being low relative to the resistance of said load c1rcu1t,

an integrating network including a capacitance connected in series with an electron discharge tube having a cathode, acontrol electro'de'and an anode, means tov apply a charging potential across said network, means to apply a portion 4of the voltage developed across said resistance between said cathode and said control electrode to control the charging current of said network substantially in proportion to the voltage developed across said resistance, and means to measure the voltage developed across said capacitance.

3. A system for developing a measuring voltjage proportional to the integral value of the product of current and time in a load circuit, said system comprising a resistance serially connected to said load circuit, the voltage developed across said resistance depending on the intensity of current flow in said load circuit, `the value of said resistance being low relative to the resistance of said load circuit, and an integrating network including a capacitance connected in series with an electron discharge tube having va control electrode, said series-connected capaciage developed across said resistance depending on the intensity of current ow in said load circuit, the value of said resistance being low relative to the resistance of saidrload circuit, an integrating network including a capacitance connected in series with an electron discharge tube having a control electrode, said seriesconnected capacitance and tube being coupled across said resistance, said control electrode being connected to a point on said resistance at which the charging current in said network is controlled substantially in proportion to the voltage developed across said resistance, and means to measure the voltage developed across said capacitance.

5. Apparatus for measuring the integral value of the product of current and time in a load circuit, said apparatus comprising a ballast resistance serially connected to said load circuit, the voltage developed across said resistance depending on the intensity at current Iiow in said load circuit, the value of said ballast resistance being low relative to the resistance of said load circuit, a capacitance having one electrode connected to one end of said ballast resistance, an electron discharge tube having a cathode, a control grid and an anode, a negative feedback resistance, said cathode being connected through said feedback resistance to the other end of said ballast resistance, said grid being connected to an intermediate point on said ballast resistto a predetermined integral value'of the product of current and time in said load circuit for actuating said switching means, said apparatus comprising a ballast resistancey seriallyV connected to said load circuit, the voltage developed across said resistance depending on the' intensity at current flow in said load circuit, the value of said ballast resistance being low relativev to the resistance of said load circuit, a capacitance havingone electrode connected' to one end of said ballast resistance, an electron discharge tube having a cathode, a control grid, and an anode, a negative feedback resistance, said cathode being connected through said feedback resistance to the other end of said ballast resistance, said grid being connected' to an intermediate point on said ballast resistance at which the charging current through said capacitance is controlled substantially in proportion to the voltage developed across said resistance, said anode being connected tothe other electrode of said capacitance, and means responsive to a predetermined value of voltage developed across said capacitance for actuating said cut-off switching means.

7. A radiographic control system comprising an X-ray device, a control discharge tube having a control electrode, a ballast resistance having an adjustable tap, a power source for energizing said X-ray device, said power source being connected to said X-ray device through said ballast resistance and said control tube, the voltage developed across said resistance depending on the intensity at current flow in said load circuit, a capacitance having one terminal connected toone end of said ballast resistance, an electron discharge tube having a cathode, a control grid and an anode, a negative feedback resistance, said cathode being connected through said feedback resistance tothe other end of said ballast resistance, said gri-d being connected to said adjustabletap to controla charging current in said capacitance substantially in proportion to the voltage developed across said resistance, said anode being connected to the other terminal of said capacitance, and means responsive to a predetermined value of voltage developed across said capacitance for applying a cut-off bias to said control electrode of said control tube.

8. A system for developing a measuring voltage proportional to the integral value of the product of current and time in a load circuit, said system comprising a resistance serially connected to said load circuit, the voltage developed across said resistance depending on the intensity at current flow in said load circuit, the value of said resistance being low relative to the resistance of said load circuit, an integrating network including a capacitance in series with an electron discharge tube having a control electrode, a source of charging potential connected across said network, and means to apply a portion of the voltage developed across said resistance to said control electrode to control the charging current of said network substantially in proportion to the voltage developed across cuit, the value of said resistance being low relative to the resistance of said load circuit, a capacitance, an electron discharge tube having Aa cathode, a control grid and an anode, a negative feedback resistance, said cathode being connected through said feedback resistance to `one end of said ballast resistance, said control grid being connected to a point of said ballast resistance at which charging current in said capacitance is controlled substantially in proportion to the voltage developed across said resistance, said anode being connected to Yone terminal of said capacitance, and a source of Ycharging potential connected between the other terminal of said capacitance and said one end of said ballast resistance.

10. A system for developing a measuring voltage proportional to the integral value of the product of current and time in a load circuit,

said system comprising a ballast resistance having an adjustable tap and serially connected to said load circuit, the voltage developed across said resistance depending on the intensity at current flow in said load circuit, the value of said resistance being low relative to the resistu ance of said load circuit, a charge capacitance, an electron discharge tube having a cathode, a' control grid, a screen grid and an anode, a negative feedback resistance, a by-pass capacitance, a source, of bias voltage, said cathode being connected through said feedback resistance to one end of said ballast resistance, said control grid being connected through said source of bias voltage to said adjustable tap to control charging current in said capacitance substantially in proportion to the voltage developed across said resistance, said screenl grid being coupled through said by-pass capacitance to said one end of said ballast resistance, said anode being connected to one terminal of said charge capacitance, and a source of charging potential having an intermediate tap, said source being connected between the other terminal of said charge capacitance and said one end of said ballast resistance, said intermediate tap being connected to said screen grid.

1l. A radiographic control system comprising an X-ray device, a ,control discharge tube having a control electrode, a ballast resistance hav- Ving an adjustable tap, a power source for energizing said device, said power source being connected to said device through said control tube and said ballast resistance, the voltage developed across said resistance depending on the intensity at current flow in said load circuitga charge capacitance, an electron discharge tube having .3 a cathode, a control grid, a screen grid and an anode, a negative feedback resistance, a by-pass capacitance, a source of bias voltage, said cathiode being connected through said feedback resistance to one end of said ballast resistance, said control grid being connected through said source of bias Voltage to said adjustable tap to control charging current in said capacitance substantially in proportion to the voltage developed across said resistance, said screen grid being coupled through said by-pass capacitance to said one end of said ballast resistance, said anode being connected to one terminal of said charge capacitance, a source of charging potential having an intermediate tap, said source of charging potential being connected between the other terminal of said charge capacitance and said one end of said ballast resistance, said intermediate tap being connected to said screen grid, and means responsive to a predetermined value of voltage developed across said charge capacitance for applying a cut-off potential to said control electrode of said control tube.

ANTONIUS WILHELMUS VINGERHOETS.

REFERENCES CTED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

